Process of making alkali subsilicates



Patented Nov. 36, 1&3?

EA'EENT success or MAKING ALKALH spe- Sm Richard Lloyd Davies, Philadelphia, Pa, assignor to Pennsylvania Salt Manufacturing @ompany, Philadelphia, Pa a corporation oil Pennsylvania No Drawing.

' 20 Gimme.

My invention relates to a novel process of manufacturing soluble alkali silicates and more particularly it relates to an economic process for the production of alkali sub-silicates with an alsell content not less than the silica content by the direct reaction of molten caustic alkali and silica-containing material.

One object or the present invention is to pro-- vide a method by which soluble alkali silicates may be easily and economically manufactured without resort to the expensive equipment and laborious steps required in either the wet digestion or the furnace-process previously employed in the production of these compounds.

A further object of the invention is to furnish a process of making alkali sub-silicates by the reaction between molten caustic soda and solid reactive silica-containing material in contradistinction to the previous processes where the reactions are carried out either in solution or by fusion in a furnace Still another object is to provide a. process by which granular or pulverulent soluble alkali silicates may be obtainedin one step at small expense for labor and with a small capital investment.

Still another object is to provide-a process for the manufacture of high grade, free-flowing stable alkali silicates of low hydration and of variable ratios of Nazi) to SiOz; for example, it is possible by this new method to manufacture the sesquisilicate with a ratio of alkali to silica (No.20 to S102) oi 1.5 to 1 and increase this through the 2 to 1 ratio of the orthosilicate and up to 8, 10 or even 40 to l in the case of detergents required in special cases, such as in bottle'washing or where a. heavy duty detergent is required. The substantially anhydrous materials obtained by the process of the present invention may be con trasted with the variety of silicates now available on the market and which contain large and varying percentages of water of crystallization.

, Other objects will be apparent from a consideration of the specification and claims.

The processes heretofore employed in the production of alkali silicates whose NazO content-is not less than the silica content, known and'referred to herein as alkali sub-silicates, have been time consuming, laborious, and expensive and have required a comparatively heavy plantinvestment. As indicated above, the sub-silicates have previously been manufactured by fusion methods, or by'wet digestion methods or a combination of the two. In the fusion method, an

- alkali carbonate and silica are heated together to a high temperature substantially above the fusion point of the system',and the fused product after solidifying is dissolved. in water and corrected to the proper alkali-silicate ratio. It is then necessary to concentrate the solution, re-

Application September 3, 1936 Serial No. 993% (or. sc -no) move the silicates therefrom by crystallization, drying, andcomminuting the crystals. In such a. process, the plant and equipment are costly, the repair charges are high due to the slagging effect on the furnace linings, and the fuel consumption is high. In the wet digestion method, a solution of water glass, or finely divided silica rendered soluble by digestion with a concentrated solution of caustic alkali, is evaporated and cooled to a suitable crystallization temperature. seeded, agitated, and cooled to remove therefrom theheat generated by the crystallization. The crystals are removed, dried, and comminuted. When water glass is employed, it'is obtained by fusing silica with an. alkaline carbonate or an alkali sulphate and carbon, followed by a special extraction process to render the silicate soluble. It is obvious that in these digestion processes the evaporation costs are high, a comparatively large plant isrequired, and the necessary digester equipment is expensive.

It is then The process of the present invention is a marked departure from the previous processes, since neither cry'stallizing tanks nor digesting apparatus is necessary. In accordance with the provisions of the present invention, the manufacture of these sub-silicates is advantageously undertaken in connection with the manufacture of caustic soda or caustic potash, and themolten caustic alkali from a caustic pot may be charged into a mixing device and the solid, reactive silicacontaining material added gradually with careful stirring. The length of time of the reaction and the'time required to produce the granular product will obviously depend on the temperature ofthe caustic soda reacted. Preferably, causticsoda of 100% purity is used at or above its melting point, in which case the reaction is a violent.

'one andis practically instantaneous. The re-' action is complete in one minute after the addition of the last of the silica-containing material and in fifteen to twenty minutes a free-flowing granular material is discharged from the mixer. Thus in a one-step process and with a small investment, it is possible to produce an excellent digestion and the furnace methods previously employed in the-manufacture of alkali sub-silicates. The present process avoids the multiple adjustments and re-adjustments oi. composition, hy dration, and concentration, as well as the seeding, crystallization, separation of the crystals, and drying required in a wet digestion method. By

sesquisilicate or orthosilicate or mixtures of these materials. If the ratio of NaaO to S102 is 2 to 1,

. a silicate is formed directly in the mixture which is from 99% to 100% soluble. The ratio of the two oxides in the compound corresponds to the orthosilicate and is technically anhydrous. When the ratio of NazO to SiOz is 1.5 to 1, a compound is formed in the mixer in which the ratio of NazO to SiOi corresponds to the sesquisilicate. If the ratios of NazO to $102 lies between the 2 to 1 and the 1.5 to 1, mixtures of the orthoandsesquisilicates will be obtained. If the ratio of NazO to S102 is higher, then higher ratio silicates or mixtures of caustic soda'and sodium silicate will be formed, which products,-as previously pointed out, are particularly applicable for use as detergents.

The term solid, reactive, silica-containing material employed herein includes silica and 'the solid water glasses where the ratio of S102 exceeds that of NaaO, for example the water glasses where the ratio of NazO to SiOz is 1 to 3.32 and 1 to 2. It is to be understood, however, that other solid compounds of NazO and SiOz where the ratio of the latter exceeds the former may be employed. The silica may be of any desired purity and of any suitable fineness to promote the reaction and may be anhydrous or a hydrated silicon dioxide. The silica may be in an amorphous form, such as opal or diatomaceous earth, or the natural crystalline forms such as rock crystal, sand, flint, sandstone or any other variety of quartz can be used. By-product amorphous or crystalline forms of silica hydrated or otherwise are also suitable sources of silica. Since in general a high purity product is desired, a relatively pure silica will be used, but it the purity of the finished silicate is not a requisite, impure silica may be used, provided that the impurities do not react at the temperature and under the conditions of .the reaction to form insoluble silicates. I

The' term molten caustic soda refers to the caustic soda which while molten at elevated temperatures is solid at ordinary temperatures. Caustic soda of 100% purity may be used, as well as molten caustic soda containing water, for example as much as approximately 15% water. Preferably, as previously stated, the molten caustic soda will possess sufficient sensible heat, as is the case when molten 100% caustic soda is used at or above its melting point, to produce a technically anhydrous product directly in, the

mixing device. The reaction between the caustic soda and the solid silica-containing material may take place at any temperature between the melting point of the caustic soda (about 318 C. for caustic soda) the melting point of the reaction product. When molten caustic soda of less than 100% NaOH is employed, the temperature and concentration thereof will determine the reaction and granulation time, and the degree of hydration of the product obtained from the mixing device. The higher the temperature and the concentration 01' the molten caustic soda. the

more closely will the product approach the teeth nically anhydrous sub-silicate, since water associated with the caustic soda is driven off by the combined effect of the sensible heat and of the heat of the reaction along with chemically comblned' water displaced from the caustic soda. As previously indicated, the process of the present invention is advantageously carried out in consolid reactive silica-containing material are mixed immediately after the removal of the desired amount of water from the caustic soda, at which point the temperature of the caustic soda is sufficiently high to cause an immediate reaction. Preferably the reaction is carried out at temperatures between approximately 300 C. and approximately 500 C.

In a typical case, and to prepare sesquisilicate of soda, 60 parts of silica are added gradually to a revolving mixer which contains 123 parts of molten caustic soda at a temperature of about 400 C., the reaction is complete in about four minutes, the mass becomes plastic during a further thirteen minutes and starts to crumble, and is discharged in a further three minutes as a free-flowing, technically anhydrous, granular material ready for the market. To prepare the orthosilicate, 60 parts of silica are added gradually to a mixer which contains parts of molten caustic soda under similar conditions to the previous example, within one minute of the addition of all of the silica the reaction is complete and in less than a total time of twenty minutes a substantially anhydrous free-flowing powder is discharged from the mixer, the material being ready for the market. To prepare the detergents with the higher ratios of sodium oxide to silica, four examples are given, also it is sometimes desirable in connection with this process to incorporate with the silicates other materials possessing somewhat similar properties, for example trisodium phosphate, disodium phosphate, sodium .carbonate, and sodium bicarbonate. Such a mixture may be. employed, for example, where water-softening properties are desired.

(1) Sodium oxide to silica-7 to 1 ratio.

(2) Sodium oxide to silica20 to 1 ratio,

(3) Sodium oxide to silica-40 to 1 ratio (4) Sodium oxide to silica-20 to 1 ratio in which Na3PO412HzO was incorporated.

In Example (1) 82 lbs. of molten caustic soda and 8.6 lbs. of silica are used; in the 20 to 1 Example (2), '82 lbs. .of molten caustic and 3 lbs. of silica are used; in the 40 to 1 Example (3), 82 lbs. of molten caustic-and 1.5 lbs of silica' are used; and in Example (4), 3 lbs. of silica are well mixed with 8 lbs of N83PO4(12H2O) and the mixture added to 82 lbs. of. the molten caustic. Each of. these mixtures is agitated from fifteen totwenty minutes and in each case a granular product is produced of excellent color and in a substantially anhydrous form. The

temperature of the molten caustic used in these mining the amount of caustic soda to be added 7 toform the sub-silicate desired.

To prepare the sesquisilicate using solid water glass, the following example may be given: 100 parts of water glass having a ratio of No.20 to S102 of 1 to 3.32 are gradually added with stir-' 7 charged from the mixer in powder form, more than 94% of which is soluble in water.

I so

To prepare the orthosilicate from a similar grade of water glass and molten caustic soda, 100 parts of the water glass are added gradual- 1y with stirring to 170 partsof molten caustic "soda, the reaction is complete in less than two minutes, and in five and three-quarter minutes a dry powdery material is discharged from the mixer, over 98% of which is soluble in water.

To prepare the sesquisilicate from another type of water glass, for example onehaving a ratio of NazO to S102 of l to 2, the following materials are charged into the mixer: 91 parts of water glass and 84 parts of molten caustic soda. The reaction is complete in less than a minute, an excellent free-flowing product being discharged from the mixer in about five minutes;

The orthosilicate of soda is prepared from this second type of water glass by 91 parts of water glass with 126%, parts'of molten caustic soda, the reaction is complete in less than a minute and a granular product in powder form is produced in about five minutes.

It is to be understood that products with a higher ratio of NaaO to S102 than those given may also be obtained by the use of the solid water glasses by a comparable process where the ratio is increased as desired, In this casealso, other materials such as the phosphates and carbonates mentioned may be incorporated in the final product.

In the foregoing examples, the olten caustic soda employedwas approximatel .100% caustic soda, and it is to be understood that ii molten caustic soda containing sometwater is used, the weight .of caustic soda added will be increased accordingly.

Considerable modification is possible in the proportions of reactive silica material and water glass employed, also the temperature of the molten caustic can be varied without departing from -the essential features of the invention.

being present in such molecular proportions that v the alkali oxide content is not less than the silicon dioxide content, reacting the mixture while stirring it at a temperature, below the melting point I of the reaction product, sufficient to form an alkali sub-silicate product, and converting the reaction mass into a solid state.

2. The process of claim 1 wherein a sodium sub-silicate product is formed by the reaction of molten caustic soda, containing not more than approximately water, and a solid, .sub-divided, silica-containing material selected from the group consisting of silica and a sodium silicate having a molecular ratio of SiOz to NazO greater than 1 to 1.

3. The process of preparing a solid, technical- 3 ly anhydrous, alkali sub-silicate product which comprises adding molten caustic alkali, containing not more than approximately 15% water, anda solid, sub-divided, silica-containingmaterial selected from the group consisting of silica and alkali metal silicate having a molecular ratio of $102 to alkali oxide greater than 1 to 1, to a reaction vessel, the reactants being present in such molecular proportions that the alkali oxide content is not less than the silicon dioxide content, reacting the mixture while stirring it at a temperature, below the melting point of the reaction product, sufilcient to free the "mixture substantially of water, and to form a technically anhydrous alkali sub-silicate product, and converting the reaction mass into a solid state.

4. The process of .claim 3 wherein a sodium sub-silicate product is formed by the reaction of moltencaustic soda, containing not more than approximately 15% water, and a solid, subdivided, silica-containing material selected from the group consisting of silica anda sodium silicate having a molecularratio of S102 to. No.20 greater than 1 to 1.

5. The process of preparing 'a solid, sodium subsilicate product which comprises adding molten caustic soda, containing not more than approximately 15% water, and a solid, sub-divided,silicacontaining material selected from the group consisting of silica and sodium silicate having a molecular ratio of S102 to NazQ greater than 1 to 1, to a reaction vessel, thereactants being present in such molecular proportions that the NazO content is not less than the S102 content,

reacting the rnlxture while stirring it at a temperature between approximately 300 C. and approximately 500" C. to form a sodium sub-silicate product, and converting the reaction mass into a solid state.

6. The process of preparing a solid, alkali subsilicate product which comprises adding molten caustic alkali, containing not more than approximately 15% water; and a solid, sub-divided, silicacontaining material selected from the group con= sisting of silica and alkali metal silicate having a molecular ratio of S102 to alkali oxide greater than 1 to 1, to a reaction vessel, thereactants being present in such molecular proportions that the alkali oxide content is not less than the silicon dioxide content,- and the caustic alkali containing sufilcient sensible heat to cause a reaction between said reactants to form a sub-silicate product without the application of further heat but being at a temperature below the melting point of the reaction product, during said reaction ,stirring the mixture to produce said product, and converting the reaction mass into a solid state.

'7. The process of claim 6-wherein a sodium subsilicate product is formed by the reaction of molten caustic soda, containing not more than approximately 15% water, and a solid, subdivided, silica-containing material selected from the group consisting of silica and a sodium silia solid, sub-divided, silica-containing material selected from the group consisting of silica and alkali metal silicate having a molecular ratio of Si02 to alkali oxide greater than 1 to 1, to a reaction vessel, the reactants being present in such molecular proportions that the alkali oxide content is not less than the silicon dioxide content and the caustic alkali containing sumcient sensible heat to cause a reaction between said reactants and to free the mixture substantially of water to form a sub-silicate product without the application of further heat but being at a a temperature below the melting point of the reaction product, during said reaction stirring the mixture to produce said technically anhydrous product, and converting the reaction mass into a solid state.

9. The process of claim 8 wherein a sodium subsilicate product is formed by the reaction of molten caustic soda, containing approximately 100% NaOH and a solid, sub-divided, silica-containing material selected from the group consisting of silica and a sodium silicate having a molecular ratio of SiO: to NazO greater than 1 .10. The process of preparing 'a solid sodium sub-silicate product which comprises adding molten caustic soda, containing not more than approximately 15% water, and sub-divided silica to a reaction vessel, the reactants being present in such molecular proportions that the HMO content is not less than the S10: content, and the caustic soda containing suflicient sensible heat to cause a reaction between said reactants to form a sub-silicate product without the application of further heat but being at a temperature below the melting point the reaction product, and-during said reaction stirring the mixture to produce said product in granular form.

11. The process of preparing a solid, technically anhydrous, sodium silicate product which comprises adding molten caustic soda, containing approximately 100% NaOH and sub divided silica to a reaction vessel, the reactants being present in such molecular proportions that the N320 content is not less than the SiO: content and the caustic soda containing sufllcient sensible heat to cause a reaction between said reactants and to free the mixture substantially of water to form a sub-silicate product without the application of further heat but being at a temperature below the melting point of the reaction product, and during 'said reaction stirring the mixture to produce said ratio or 2 to 40 Naomi 102.

15. The process of preparing a solid, sodium sub-silicate product which comprises adding molten caustic soda, containing not more than approximately 15% water, and solid, sub-divided, sodium silicate having a molecular ratio of S:

to Na-.-O greater than 1 to 1, to a reaction vessel,

the reactants being present in such molecular proportions that the No.20 content is not less than.

the S10: content, and thecaustic' soda containing sumcient sensible heat to cause a reaction between said reactants to i'orm'a sub-silicate product without the application of further heat but being at a temperature below the melting point of the reaction product; and during said reaction stirring the mixture to produce said product in granular form.

16. The process ,of preparing a solid, technically anhydrous, sodium silicate product which comprises adding molten caustic soda, containing approximately 100% 119.011 and solid, sub-divided, sodium silicate having a'molecular ratio 01-810: to NazO greater than 1 to 1, to a reaction vessel, the reactants being present in such molecular proportions that the NazO content is'not less than the SiOa content and the caustic soda containing suiflcient sensible heat to cause a reaction between said reactants and to free the mixturesubstan- ,tially of water to form a sub-silicate product without the application or iurther heat but being at a temperature below the melting point of the reaction product, and during said reaction stirring the mixture to produce said technically anhydrous product in granular form. v

17. The process of claim 16 wherein a technically anhydrous, sodium sesquisilicate is formed mate molecular ratio of 1.5 119.20 to 1 SiO:'.-

18. The process of claim 16 wherein a technically anhydrous, sodium orthosilicate is formed by having the reactants present in the approximate molecular ratio of .2 NaaO t0 1 $102.

19. The process of preparing a solid sodium sub-silicate product which comprises adding molten caustic soda, containing not more than approximately water, and a solid, sub-divid ed, silica-containing material selected from the group consisting oi silica and sodium silicate havsub-silicate product which comprises adding. molten caustic soda, containing not more than approximately 15% water, and a solid, sub-divided, silica-containing material selected from the group consisting or silica and sodium silicate having a molecular ratio of $102 to NaaO greater than 1 to 1, and a material selected from the group consisting of a sodium carbonate, a sodium phosphate, to a reaction vessel, the "caustic soda and silica-containing material being present in molecular proportions to form a sub-silicate having a molecular ratio of N820 to $10: not less than 1 to 1, and the caustic soda containing suflicient sensible heat to cause a reaction between the caustic soda and the silica-containing material to form a sub-silicate product'without the application of further heat but being at a temperature below the melting point of the reaction product, and during said reaction stirring the mixture to produce said'product in granular form.

' RICHARD LLOYD DAVIES.

.by having the reactants presentin the approxi- Patent No. 2,100,91 11,

, CERTIFICATE 0F' CORRECTION.

v November 50 1937 a RICHARD LLOYD DAVIES.

It ishereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows Page 2, first colmnn; line 12, forthe word "mixture" read-mixer; page 1 first column, I

- line 67, claim 15, for 810 read S10 and that the said Letters Patent should be read with these corrections therein that the same may conform to the record .of the case in the Patent Office. Signed and sealed this 26th day of April, A. D. 1938.

. Henry Van Arsdale, (Seal) I Acting Commissioner of Patents. 

